1. Field of the Invention
The present invention relates to control on acquisition of color value information in an image forming apparatus that performs color balance correction based on color value information of an image formed on a recording material.
2. Description of the Related Art
There is demand for improvements in the image quality of images output from color image forming apparatuses such as color printers and color photocopiers. The tone of the density of the output images and the stability thereof are important elements that determine the image quality. Hence, the color image forming apparatuses need to suppress fluctuations in the density caused by environmental changes and prolonged use.
In view of this, Japanese Patent Laid-Open No. 2004-245931 discloses a configuration in which, after forming toner images for color correction using toner of each color (hereinafter referred to as “patch images”) on a recording material, color values of the patch images formed on the recording material are detected so as to correct color values of toner images. In Japanese Patent Laid-Open No. 2004-245931, detection of a color value of each patch image for color correction is started based on a time period that has elapsed since detection of a reference patch image. This is described more specifically below with reference to FIG. 16.
As shown in FIG. 16, following a reference patch image 12a that can be acknowledged without fail, a plurality of patch images 10a, 10b and 10c for color correction are formed on a recording material. Note that in FIG. 16, the patch images 10a and 10c have high reflectance, whereas the patch image 10b has low reflectance. In FIG. 16, each of T10a, T10b and T10c represents a time period from when the start of the reference patch image 12a is detected, to when the acquisition of color value information of the corresponding patch image 10a, 10b or 10c is started. Note that each of Ma1, Mb1 and Mc1 represents a top margin section starting from the top edge of the corresponding patch image 10a, 10b or 10c, and ending when the acquisition of color value information is started. Similarly, each of M0, Ma2, Mb2 and Mc2 represents a bottom margin section.
FIG. 16 depicts a case where the color value information is acquired four times from each patch image. Note that in FIG. 16, Sa1-Sa4, Sb1-Sb4, and Sc1-Sc4 represent sections in which four pieces of color value information are acquired from the patch images 10a, 10b and 10c, respectively. It should be noted that the length of each section in which the color value information is acquired is determined in accordance with the reflectance. Here, the color value information is acquired multiple times for the purpose of correcting variations therein.
When using the method described above with reference to FIG. 16, the length of patch images in a conveyance direction of the recording material should be determined while taking the following factors into consideration: variations in the outer diameters of conveyance rollers that convey the recording material; fluctuations in the speed of conveying the recording material caused by environmental changes; influence of contraction of the recording material occurring when the recording material passes a fixing unit; and influence of expansion and contraction of an image occurring before the image is formed on the recording material. That is to say, the length of patch images should be determined while taking into consideration the top and bottom margins such that color value information can be acquired from each patch image without fail, even if the above-listed variations and fluctuations occur.
In order to correct the image quality to a high degree of precision so as not to make the user realize fluctuations in the density and color, it is necessary to detect a large number of color values by using a wide variety of patch images with different densities and colors. However, an increase in the number of patch images causes an increase in the sum of the lengths of the margin sections. This results in an increase in the size of a recording material required for forming the patch images, or an increase in the number of recording materials required therefore.